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      Hexavalent chromium in drinking water: Chemistry, challenges and future outlook on Sn(II)- and photocatalyst-based treatment

      research-article
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      Frontiers of Environmental Science & Engineering
      Higher Education Press
      Chromium, Chemistry, Treatment, Future outlook

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          Abstract

          Chromium (Cr) typically exists in either trivalent and hexavalent oxidation states in drinking water, i.e., Cr(III) and Cr(VI), with Cr(VI) of particular concern in recent years due to its high toxicity and new regulatory standards. This Account presented a critical analysis of the sources and occurrence of Cr(VI) in drinking water in the United States, analyzed the equilibrium chemistry of Cr(VI) species, summarized important redox reaction relevant to the fate of Cr(VI) in drinking water, and critically reviewed emerging Cr(VI) treatment technologies. There is a wide occurrence of Cr(VI) in US source drinking water, with a strong dependence on groundwater sources, mainly due to naturally weathering of chromium-containing aquifers. Challenges regarding traditional Cr(VI) treatment include chemical cost, generation of secondary waste and inadvertent re-generation of Cr(VI) after treatment. To overcome these challenges, reductive Cr(VI) treatment technologies based on the application of stannous tin or electron-releasing titanium dioxide photocatalyst hold extreme promise in the future. To moving forward in the right direction, three key questions need further exploration for the technology implementation, including effective management of residual waste, minimizing the risks of Cr(VI) re-occurrence downstream of drinking water treatment plant, and promote the socioeconomic drivers for Cr(VI) control in the future.

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          Most cited references24

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          The Technology Horizon for Photocatalytic Water Treatment: Sunrise or Sunset?

          Advanced oxidation processes via semiconductor photocatalysis for water treatment have been the subject of extensive research over the past three decades, producing many scientific reports focused on elucidating mechanisms and enhancing kinetics for the treatment of contaminants in water. Many of these reports imply that the ultimate goal of the research is to apply photocatalysis in municipal water treatment operations. However, this ignores immense technology transfer problems, perpetuating a widening gap between academic advocation and industrial application. In this Feature, we undertake a critical examination of the trajectory of photocatalytic water treatment research, assessing the viability of proposed applications and identifying those with the most promising future. Several strategies are proposed for scientists and engineers who aim to support research efforts to bring industrially relevant photocatalytic water treatment processes to fruition. Although the reassessed potential may not live up to initial academic hype, an unfavorable assessment in some areas does not preclude the transfer of photocatalysis for water treatment to other niche applications as the technology retains substantive and unique benefits.
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            Genesis of hexavalent chromium from natural sources in soil and groundwater.

            Naturally occurring Cr(VI) has recently been reported in ground and surface waters. Rock strata rich in Cr(III)-bearing minerals, in particular chromite, are universally found in these areas that occur near convergent plate margins. Here we report experiments demonstrating accelerated dissolution of chromite and subsequent oxidation of Cr(III) to aqueous Cr(VI) in the presence of birnessite, a common manganese mineral, explaining the generation of Cr(VI) by a Cr(III)-bearing mineral considered geochemically inert. Our results demonstrate that Cr(III) within ultramafic- and serpentinite-derived soils/sediments can be oxidized and dissolved through natural processes, leading to hazardous levels of aqueous Cr(VI) in surface and groundwater.
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              Chromate removal from aqueous wastes by reduction with ferrous ion.

              L Eary, D. Rai (1988)
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                Author and article information

                Contributors
                haizhou@engr.ucr.edu
                Journal
                Front Environ Sci Eng
                Front Environ Sci Eng
                Frontiers of Environmental Science & Engineering
                Higher Education Press (Beijing )
                2095-2201
                2095-221X
                10 August 2020
                2020
                : 14
                : 5
                : 88
                Affiliations
                GRID grid.266097.c, ISNI 0000 0001 2222 1582, Department of Chemical and Environmental Engineering, , University of California at Riverside, ; Riverside, CA 92521 USA
                Article
                1267
                10.1007/s11783-020-1267-4
                7439242
                32839673
                f35ff6a3-4854-4e0e-b48d-be0c2fdae587
                © Higher Education Press 2020

                This article is made available via the PMC Open Access Subset for unrestricted research re-use and secondary analysis in any form or by any means with acknowledgement of the original source. These permissions are granted for the duration of the World Health Organization (WHO) declaration of COVID-19 as a global pandemic.

                History
                : 8 May 2020
                : 19 June 2020
                : 29 June 2020
                Categories
                Review Article
                Custom metadata
                © Higher Education Press 2020

                chromium,chemistry,treatment,future outlook
                chromium, chemistry, treatment, future outlook

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